For electrical equipment that uses batteries and requires high power, such as electric or hybrid vehicles, the battery system will often contain multiple battery packs, only one of which will be powering the system at any time. The battery system therefore needs be able to switch from one pack to another in a manner that protects the battery packs and contactors, especially while the vehicle is in operation. Conventional systems with multiple packs generally switch to a different pack by shutting the load off completely regardless of the state of the operation and waiting for a long period to switch over. This can result in potentially dangerous problems including long switchover times that disable the vehicle operation for a long duration or switch over while the vehicle is midst of acceleration.
An example of a battery system for an electric vehicle with N battery packs is shown in FIG. 1, where N is 2 or greater. In this system, only one of the battery packs is connected to the vehicle load at a time. When the charge in battery pack 1 is exhausted, the system may switch to the next battery pack with available charge.